Hue-Saturation adding artifacts to some images

[Ofnuts]

(08-27-2021, 01:57 AM)PixLab Wrote: try the ofnuts's red filter that rich2005 is speaking about,

Some filters are not by yours truly

[denzjos]

Maybe the Krikor plugin can help you.
https://gimplearn.net/viewtopic.php/GIMP...7ba0c0824d
If the result is to dark in the shadow areas, then :
- make a new layer from the visible (right click on the layers dock : New from Visible)
- desaturate this layer : Colours / Desaturate / Desaturate
- set the layer mode on this layer on 'Soft Light'
- if not satisfied, use the Opacity slider on this layer
- if not satisfied with the color, use the levels : Colours / Levels ( Value :  blue / green /red 'Input Levels' slider)     
After Krikor plugin :
   
After 'Soft Light' layer
   
Little levels correction :
   

[denzjos]

Another way to correct the photo is by using the black, grey and white color pickers from the 'Colour / Levels'. First pick a dark area with the black picker, the white with te white picker and then go around on the photo with the grey picker until you find a place to click where you are satisfied with the result. An example (upper photo is manipulated, the bottom one is the original)
   

[cansu]

(08-25-2021, 07:20 PM)Mango Turtl Wrote: I've noticed that on some images, specific parts of the image will occasionally become black and grainy when the Hue-Saturation feature is used. Is there any fix for this? Does anyone know what causes it? I've tested a little bit, and it seems that the black artifacts always appear, no matter what I do with the Hue-Saturation feature.

In the first attached image, I have not used Hue-Saturation yet. Some areas of the coral are naturally in shadow, but still have a color that makes sense and looks pretty good. In the second attached image, I tried to use Hue-Saturation to remove some green tint from the image. It worked, but left some areas of the coral that were previously in shadow with a black, grainy look.

Hey it's been a while but have you found any solution to this? I'm having the same problem and no they're not underwater photos so it doesn't have anything to do with that. It's not about the photo's properties at all, I think. Cause as you said, the artifacts don't come along with the edits I do, they appear the moment I click on "color balance" on the menu, and before I start editing. So I thought it's a bug as well.

[Ofnuts]

It is pretty much expected in the darker areas. If you have for instance something dark purple (so Red and Blue have low values, and Green is 0 or close to), and what to make it greener, you have to reduce Red and Blue, that becomes very close to 0, but your Green won't change (if 0) or won't change much (if slightly above 0), so you don't get a dark green but an even darker pixel.

You can avoid this if you use Curves/Levels and work channel by channel, but in that case you may get color shifts where you don't want.

All a matter of compromises, and using the right tools.

Some of the problem comes from using 8-bit images. But you work with high-bit-depth this problem occurs in a more diffuse and less noticeable way.

[denzjos]

Lot of colour noise (high iso?). I tried G'Mic-Qt / Repair / Smooth [Thin Brush], then 'Filters/Enhance/Sharpen (Unsharp Mask) and the copy the layer and set layer mode to 'screen' with a opacity 50% .